(1) Field of the Invention
This invention relates to a microwave heating apparatus, namely a microwave oven, for cooking foods and the like, in which electromagnetic high frequency waves are used to rapidly cook the foods and more particularly to a static energy delivery system for distributing microwave energy for efficient operation and improved cooking results.
(2) Description of the Prior Art
In using microwave ovens for heating or cooking, an ideal system of energy distribution would evenly distribute microwave energy across those portions of the cavity in which food was located. Since food is normally located in only a limited area of the oven it would also be desirable to maximize the energy in the portion of the cavity in which the food is to be located. Microwave ovens have employed numerous types of feed and distribution systems for this purpose.
In British Pat. No. 1,407,852 there is disclosed a microwave oven which utilizes "near field" effects of electromagnetic radiation to heat the foods. Near field heating is known to given considerably better results in heating foods having greatly differing dielectric properties. In order to accomplish this the food is maintained in close proximity with a radiation element, preferably less than one wavelength of the exciting electromagnetic energy. A waveguide is located underneath the food which has a plurality of slots. A food shelf is located directly over the waveguide to position the food in the near field. A removable reflector is located above the shelf by a distance not more than a wavelength of the applied microwave radiation. With the reflector in place, the oven constitutes a near field applicator; with the reflector removed, a resonance applicator.
U.S. Pat. No. 3,810,248 discloses a microwave apparatus in which heating of food is accomplished by placing the food in a support directly over slotted openings in a waveguide. Food is placed in a container so as to be heated concurrently by microwave energy acting directly on the food and by microwave energy acting indirectly by heating a radiation-absorbing layer in contact with the food.
U.S. Pat. No. 3,851,133 shows a microwave oven design directed to reducing the problem of uneven heating of foods in a microwave oven cooking cavity by providing an antenna chamber disposed adjacent the cooking cavity with microwave energy being introduced into the cavity through radiation slots disposed on the side of the cavity adjacent the antenna chamber. The antenna takes the form of radially extending arms rotating about a common axis.
U.S. Pat. No. 4,019,009 discloses a microwave oven which heats food by subjecting it to a microwave field generated by a surface wave transmission line comprising a slotted wall. The food may also be concurrently subjected to the far field effects of additional transmissions into a resonant heating cavity.
Other well known energy distribution microwave ovens rely heavily on the use of rotating devices within the cooking cavity. Most typically, a rotating mode stirrer is employed, the mode stirrer having blades and being driven by a motor cyclically varying the modes set up in the resonant cavity to thereby more evenly distribute the heating effect. Rotating food trays and rotating antennas have also been employed. Each of these approaches introduces motors, couplings and other complications, increasing the cost and reducing the reliability of the overall system.